That looks like a cast piston. A forged piston will bend, but not snap. A rule of thumb is a cast piston will run 10 psi of boost fairly reliably. But once 13psi is hit, then the boost (not detonation) will break off sections of the ring lands because of pressure forces. Detonation can damage the piston at a much lower boost level. Forged pistons usually will melt where the piston got too hot and exceeds the materials temperature threshold. Did you do something that was out of the ordinary?